1. Field of the Invention
The present invention relates to fluid powered motors and, more specifically, to the cooling of or dissipation of heat from such motors.
2. Description of the Prior Art
A wide variety of fluid-powered tools, such as air tools, utilize a rotary air motor which has a rotor mounted eccentrically in a circular bore in a cylindrical liner which may, in turn, be mounted in a tool housing. Movable vanes mounted radially in the rotor extend outwardly to contact the inner surface of the bore and provide sealing for the driving fluid, typically compressed air. Inlet and exhaust ports are provided in the housing to allow the driving fluid to enter the bore, drive the rotor and exhaust from the motor. The rotor is usually mounted in bearings in a pair of end plates at opposite ends of the liner. As the rotor rotates, the vanes cooperate with the liner to define a plurality of rotating and variable volume fluid chambers which sequentially communicate with the inlet and exhaust ports. In such motors, the driving fluid typically also serves to cool the motor.
The fluid typically enters at the rear end of the tool and motor. Heretofore, there have generally been two types of exhaust arrangements, viz., front exhaust and rear exhaust. In the front exhaust arrangement the fluid exits the motor at the front end thereof, i.e., the end which carries the output shaft, while in the rear exhaust arrangement, the fluid exits the motor at the rear end thereof, i.e., the same end that the fluid enters.
In typical rear exhaust air tools, the compressed air enters an air motor chamber and, after a predetermined angular rotation, which may be approximately 140.degree., the air exhausts from an exhaust port in the rear end plate. As the air motor operates, the rotor rotates at a relatively high speed, which may be approximately 20,000 rpm. The centrifugal force on the vanes drives them into frictional engagement with the cylindrical liner, generating heat. The rear exhaust motor provides good cooling of the rear end of the motor, since the compressed air is relatively cool when it enters and the expansion of the air upon exhausting back to atmospheric pressure provides a further cooling effect. However, this type of motor does not provide effective cooling of the front end of the motor. This results in a hot front end problem, wherein the front end of the motor may become sufficiently hot to give an operator first degree burns if he touches the front end of the tool and to cause front bearing lockup of the rotor.
The hot front end problem can be alleviated by the use of a front exhaust motor, wherein exhaust ports are provided at the front end of the tool, so that the expanding, exhausting air cools the front end of the tool. However, if air is exhausted only at the front end plate and not at the rear end plate, it generates a high back pressure, resulting in lowered motor output.
It is known to provide simultaneous exhaust at both the front and rear ends of the motor. While this tends to alleviate the back pressure problem, the majority of the air takes the shortest path to the rear exhaust port and exhausts through the rear end plate. Thus, such tools may still suffer from the hot front end condition.